1. Field of the Invention
The present invention relates to a hybrid vehicle having a plurality of power sources. More specifically, the present invention relates to a series hybrid vehicle equipped with an engine, a first rotary electric machine and a second rotary electric machine.
2. Background Information
A series hybrid vehicle is a useful method of extending the cruising distance of an electric automobile driven by an electric motor. The typical series hybrid vehicle has an electric motor that is operated in series with an engine that has a generator for charging an onboard battery while the vehicle is traveling. In such series hybrid vehicles, it is typical for the engine to be stopped when the battery is sufficiently charged and for the engine to be operated to drive the generator when the charged condition of the battery starts to become insufficient. In such a case, the engine is basically operated at its rated capacity, and thus, an engine having a relatively small output can be used. At the same time, the generator has a relatively small generating capacity in keeping with the output of the engine. In short, the cost of conventional series hybrid vehicles is held in check by reducing the size of the engine and generator.
In view of the above, there exists a continuing need for an improved hybrid vehicle. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
It has been discovered that in conventional series hybrid vehicles, as mentioned above, the engines have completely different specifications from those used in other common vehicles, i.e., vehicles installed with mechanical transmissions. It is a major disadvantage to have to produce small quantities of engines having special specifications. Furthermore, in order to provide a plurality of series hybrid vehicle models having different characteristics, it is necessary to prepare engines and generators matched to each set of characteristics. Thus, hybrid vehicle models having different characteristics make it even more difficult to lower the cost of the series hybrid vehicle.
In view of the problems associated with the prior art, one object of the present invention is to employ mass production to reduce the cost of series hybrid vehicles and make it easier for series hybrid vehicles to become popular.
With this arrangement, the maximum output of the second rotary electric machine (which mainly generates the vehicle driving power) and the maximum generated electric power of the first rotary electric machine (which mainly generates electricity) are substantially equal. Consequently, it is possible to drive the vehicle at maximum output (i.e., run the second rotary electric machine at maximum output) at all times regardless of the storage status of the electric storage device installed between the two rotary electric machines. Also, the capacity and maximum output of the electric storage device can be set freely. For example, installation of the electric storage device can be eliminated or an electric storage device having a very small capacity and maximum output can be installed. In such a case, the first rotary electric machine and second rotary electric machine are used together simply as a transmission; this kind of series hybrid vehicle can be substituted for vehicles that use mechanical transmissions.
Meanwhile, if an electric storage device having a relatively large capacity and maximum output is installed in the vehicle, a similar fuel efficiency improvement effect to that of conventional series hybrid vehicles can be obtained. Furthermore, the characteristics of the series hybrid vehicle can be changed easily by changing the capacity and maximum output of the electric storage device installed. In short, the present invention makes it possible to use engines and electric rotating devices having the same specifications to manufacture vehicles that are equivalent to vehicles installed with conventional mechanical transmissions as well as series hybrid vehicles that are intended to improve fuel efficiency. The cost increase required for improving the fuel efficiency can be limited to the cost increase associated with the electric storage device.
With this arrangement, a single casing housing both the first and second rotary electric machines can be handled in the same manner as a conventional mechanical transmission, making it possible to avoid extensive modification of the manufacturing process. Also, since it is not necessary to change the shape of the casing in response to the existence or capacity of the electric storage device, a single common casing and a common vehicle-side structure for mounting the casing can be used for all vehicle models. Thus, the present invention enables further cost reductions.
The foregoing can basically be attained by a hybrid vehicle comprising an engine, a first rotary electric machine and a second rotary electric machine. The engine has an output shaft. The first rotary electric machine has a maximum generated electric power and is operatively coupled to the output shaft of the engine. The second rotary electric machine has a maximum output power and is electrically coupled to the first rotary electric machine and operatively coupled to a drive wheel of the hybrid vehicle,
The maximum generated electric power of the first rotary electric machine is substantially equal to the maximum output power of the second rotary electric machine.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.